Avalanches can cause catastrophic damage to homes, habitat and property, as well as cause human deaths. Avalanches can cause flash floods if the debris reaches rivers or lakes and causes the water level to rise. Additionally, avalanches cause economic problems, as communities must spend considerable resources to rectify the damage caused by the falling snow and ice.
There are four basic types of avalanches. Loose snow avalanches occur after fresh snowfall begins tumbling down a steep mountain face. Slab avalanches occur when an underlying block of snow or ice dislodges and falls down the mountain. Powder snow avalanches contain loose snow on top and a slab of ice or snow at the bottom. Wet snow avalanches fall slowly down a hill, slowed by the friction created. Powder snow avalanches are the most dangerous type, and such avalanches may reach 190 miles per hour in exceptional cases. Powder snow avalanches cause a large number of fatalities.
A number of different factors may cause avalanches. Human activity is frequently implicated in their occurrence, especially when heavy machinery causes excessive vibration. Weather can also cause avalanches, especially high winds or heavy rains. Excessively high temperatures can also cause portions of the snow to melt, yielding dangerous avalanches.